[electrum] build: use pyca/cryptography release version

Summary:
We previously switched the cryptography dependency to the development
branch to get reproducible builds using https://github.com/pyca/cryptography/pull/10627

This change has now been put into the 43.0.0 release so we switch to 43.0.1

This makes the AppImage build faster and more reliable (the pip install via github for this package often times-out)

This is a backport of electroncash#2902

Test Plan: contrib/build-linux/appimage/build.sh

Reviewers: #bitcoin_abc, Fabien

Reviewed By: #bitcoin_abc, Fabien

Differential Revision: https://reviews.bitcoinabc.org/D17790